The liberal party Sinn Fein measure was defeated by a 51 to 43 vote. It is the third time in the last 18 months that Northern Ireland’s parliament rejected a gay marriage measure.

The human rights organization Amnesty International condemned lawmakers who used their veto on the measure, saying they were "like latter-day King Canutes, trying in vain to hold back the tide of equality."

"States may not discriminate with regards to the right to marry and found a family on the basis of sexual orientation or gender identity," Amnesty’s program director in Northern Ireland, Patrick Corrigan, said. "That obligation is clear in international law. This means that marriage should be available to same-sex couples in Northern Ireland, just as it is now in England and Wales and will shortly be in Scotland."

Corrigan added there will be legal action because the measure was voted down.

"With politicians continuing to block equality, it is now inevitable that same-sex couples in Northern Ireland will take a legal challenge on the basis of inferior treatment with regards to the right to marry and found a family," he said.

The Guardian writes:

Under the rules of the Stormont assembly, legislation cannot pass if the representatives of one community refuse to support a new bill, which ensures no one section of the divided populace can impose laws on the other. Before the vote the Catholic hierarchy wrote a letter to every assembly member urging them to reject the bill.

In the letter, the Catholic Bishops in Northern Ireland voiced their "concern that the marriage equality motion undermines a key foundation of that common good."

"We say this not only out of religious conviction, but also as a matter of human reason. Religious and non-religious people alike have long acknowledged and know from their experience that the family, based on the marriage of a woman and a man, is the best and ideal place for children," the letter reads. "It is a fundamental building block of society which makes a unique and irreplaceable contribution to the common good. It is therefore deserving of special recognition and promotion by the state."

The letter adds: "The proposed marriage equality motion before the assembly effectively says to parents, children and society that the state should not, and will not, promote any normative or ideal family environment for raising children. It therefore implies that the biological bond and natural ties between a child and its mother and father have no intrinsic value for the child or for society. As Pope Francis stated recently, ’we must reaffirm the right of children to grow up in a family with a father and a mother capable of creating a suitable environment for the child’s development and emotional maturity.’"

Last December, a ban prohibiting same-sex and unmarried couples from adopting children in Northern Ireland was lifted.